The Unfair Equivalent Exchange
by The Wizard Rider
Summary: When Roy Mustang regains his sight, he is forced to pay another price - even though he has the Philosopher's Stone. Now, with the help of Riza Hawkeye, the Elric brothers and other faces brought into the conflict of the Promised Day, they must all help to regain the Flame Alchemist's memory. Post-FMA:Brotherhood/Manga storyline. Eventual Royai fluff, Amnesia!Roy, Parental!RoyEdAl
1. Chapter 1

_**Summary:**_ _ **When Roy Mustang regains his sight, he is forced to pay another toll, even though he has the Philosopher's Stone. Now, with the help of Riza Hawkeye, the Elric brothers, and other faces brought into the conflict of the Promised Day, they must all help to regain the Flame Alchemist's memory.**_

* * *

 _ **Well, here is my first Fullmetal Alchemist fanfic that isn't a one-shot. Yay! This is set at the ending of Fullmetal Alchemist:Brotherhood/Manga (after Promised Day), so those who haven't reached up to this part/haven't watched Brotherhood or read manga, there will be spoilers. There will be eventual Royai, and instead of Parental!Roy (I LOVE THEM FICS), it'll be the Elric brothers guiding Mustang. Could get a little angsty in future. And cross-posted on AO3 under 'TheWizardDragonRider', if anyone wants to check it out.**_

* * *

 _ **Chapter 1**_ _ **\- Regaining Sight**_

* * *

"Here is the Philosopher's Stone." I heard Tim Marcoh's voice, the alchemist who possessed the Philosopher's Stone, reaching my ears. "You may have your eyesight back... but only if you help to restore Ishval with it."

I couldn't believe my ears. _A Philosopher's Stone?!_ I'd never bothered in wanting it. In fact, I'd heard it only once during my alchemy apprenticeship, and I never bothered to think about it again. Then, when the Elric brothers had came into my life, with the older brother, Edward, becoming a State Alchemist with the codename _Fullmetal_ , with he and his younger brother Alphonse seeking it in order to return their broken and stolen bodies after their failed human transmutation, I was drawn into a plot. A plot of Homunculi - which had Philosopher's Stones at their core, the Stones themselves, and our country in the middle of a devastating plot. A plot to use every single Amestrian soul as energy in order to create the perfect Philosopher's Stone for the Homunculus Father.

I'll never forget that day. It was called the _Promised Day_ by the Homunculi, and we, who were in the midst of its battle, call it that today. I remember finding out the true killer of my best friend, Maes Hughes - Envy - and myself in a berserk rage, ending with Envy killing himself. The day Edward Elric had defeated Father with his bare fists, with people calling out his name to give him support.

I was one of them. I was also one of the five human sacrifices - me, Roy Mustang, the Flame Alchemist; the Elric brothers, Edward and Alphonse; their alchemy teacher, Izumi Curtis; and their father, Van Hohenheim. We were used as sacrifices because we had enough power to activate the circle. And how we had enough power? We had all gone through the portal by committing a taboo.

Me - I'd never wanted to commit a taboo! I remember Pride and Wrath, the two Homunculi under the disguise of Fuhrer Bradley and his son, Selim, forcing me to commit the sin of human transmutation, even slitting the throat of my beloved Riza Hawkeye. She had survived the battle, thank goodness, and I refused. So they opened the Gate another way and forced me through instead.

That had led me to meet Truth, as the Elric brothers and their teacher had done before. He had forced me through his Gate of Truth, which held all the alchemical secrets of the world, which led those three alchemists to transmute without a circle.

But the law of equivalent exchange is what alchemists live and work by. Truth did not care whether I did the taboo or not. I had seen through the Gate and lived; so he charged me a toll. He took away my eyesight, and I was sent straight to Father, alone and blind. We activated the Nationwide Transmutation Circle against our will, and Father's plan had almost succeeded, but thanks to the Alkahestric Reverse, with the help of the work of Scar's brother and the Elric brothers' father, Van Hohenheim, it failed, and the souls of the Amestrians returned to their bodies.

We continued to fight until the very end, I remember that.

Edward beat Father - who had now swallowed the power of God and Truth and had become a perfect being - with his bare fists. I didn't see it, but I remember how we had all yelled Fullmetal's name, which had given him support and strength.

It had only been a day, the Promised Day was, only a day that I lost my sight, but I remember it was the darkest time of my life (no pun intended). Now, it was just a day after the final battle, and Dr Marcoh, along with my old 'buddy', Dr Knox, had offered me the Philosopher's Stone.

 _The Stone…_ it had been made out of countless human souls. The thought of it scared me. But it could heal me… and I remembered my friend 2nd Lieutenant Havoc, who had lost all contact with his legs… I remembered how I had captured Gluttony, with the hope of using the Stone to heal him…

"Sir, do it." I heard Riza Hawkeye's voice next to me. Of course, I couldn't see her current condition, but both she and the doctors had assured me she was fine. She'd survive her injuries. Thank God. I felt her smile to me, even though I couldn't see it, and I smiled back, and nodded.

"Alright." I heard scuffling noises, and a hand clasping my arm, but I took it away, and said. "No."

I didn't see it, but I knew that the people around the room were shocked; my friends and subordinates, Breda, Falman and Fuery, and the doctors, and Hawkeye. I smiled, and said, "Wait. Not me yet. I want you to heal someone, a friend of mine, before you heal me."

"Who?" asked Marcoh.

"Havoc," I replied firmly. "Jean Havoc, he's a friend. He can't feel his legs at all. Please, help him."

I heard the doctors step back. "Alright," replied Marcoh.

"Wait, the Stone _can_ heal Havoc, right?"

"The Stone can give back feeling to his legs," replied Marcoh. "Then he must do the road to recovery on his own."

I sighed in relief. That was good to hear. But Marcoh was wrong in one part. Havoc wouldn't be alone. He'd have Breda, he'd have the whole team, he'd have me.

"We'll be leaving you with your friends now," said Marcoh, and I heard the door close with a creak and a soft slam at a close distance. I heard Breda's voice.

"Sir, that was a good thing to do."

I nodded. "Yeah, but I couldn't stand the fact that I'd be healed, and I'd only be waiting a whole day, while Havoc's been waiting for months, and he wouldn't get healed."

"That was thoughtful, sir," said Hawkeye.

"I can use the Stone to heal you too, before me, you know, Lieutenant Hawkeye."

I heard her chuckle. Man, I hadn't heard her chuckle like that for a while. "No, sir. You need it more. The doctors say with proper rest, I'll heal on my own."

"You sure?"

"I'm sure."

"Ooh, the Colonel's caring for his little Lieutenant," teased Fuery.

I felt my cheeks flush. "I care for all my subordinates. Hawkeye's one of 'em. I care about you guys too, you know."

There was silence. Until I heard Breda's voice.

"Sir, we can call Havoc, right? To Central?"

"Oh, right, do that now."

 _0-0-0-0-0-0-0-0_

Marcoh said he was drawing a transmutation circle around me, who was sitting cross-legged on the ground. I was nervous for this, completely nervous. A little voice nagged at the back of my head: _What if this doesn't work?_

 _Shut up, you,_ I replied mentally, and the voice stopped, but always came back sooner or later.

I knew my subordinates were nervous. I think Hawkeye was extremely anxious for me, too. I felt a hand on my shoulder, and her voice. "Don't worry. It'll be okay."

I hoped she was reassuring herself as well as me. I nodded, and said, "Hawkeye, can I ask a favour of you?"

She could've seemed shocked, or probably expected this, but I couldn't see her expression, because, well… I was blind. "Go ahead, sir."

"Hawkeye… 1st Lieutenant Riza Hawkeye… can I… well…"

"Yes, sir? We haven't got much time."

I took a deep breath. "When I get my sight back… please, can you be the first sight I see? You were the last person I saw before my sight was taken away, and now, when I get my sight back, I want you to be the first person."

If she wasn't shocked about the fact I had asked her a favour, she was probably astounded about what the favour was. She placed a hand on my shoulder again. "Of course, sir."

Marcoh slipped the Philosopher's Stone in my hand I knew it was blood-red, though I couldn't see it; but it felt smooth against my palm. "Are you ready?" he asked, his voice barely a whisper.

Taking a deep breath straight from the lungs, I nodded. "Yeah, I'm ready."

"Good luck, sir," said Breda. "Havoc sends his regards."

"Yeah," agreed Fuery. "We'll see you with your eyesight again!"

"And when that happens, we'll be standing here," said Falman. "Our Colonel Roy Mustang."

I nodded and beamed. That gave me great support. I couldn't wait to see my subordinates, my friends again. And Hawkeye… she'd be the first person I'd ever see.

I addressed Marcoh: "Do it," and he nodded. Suddenly, I felt as if my soul was separating from my body, and I turned unconscious.

 _0-0-0-0-0-0-0_

"So, you're here to retrieve your sight, Roy Mustang?" I heard a familiar voice leer.

I sat up immediately. I remembered him. After all, it had only been two days since that happened.

"Truth," I said, "Let me have my eyesight back. I have payment." I held out the Philosopher's Stone. "I remember the law of Equivalent Exchange."

"Remember, huh?" I heard Truth. "Actually, that gives me… alright, Roy Mustang, your eyesight will be returned to you." I felt the Philosopher's Stone leave my palm, but it didn't take a genius to figure out where it went.

Then I fell into unconsciousness once again.

 _0-0-0-0-0-0-0_

I woke up, and opened my eyes. Where was I? I didn't know. I looked up, and noticed a blonde-haired woman, in her mid-to-late twenties, with long hair. _She was beautiful,_ that was one of my first thoughts about her. Her throat was bandaged. What had happened to her?

She held out a bandaged hand to me. "Welcome back, sir."

I didn't understand. Who was this woman? Why did she call me 'sir'? I looked around. I saw an extremely old man smiling at me, saying, "The Stone worked, didn't it?" and three men all grinning at me, saying: "Welcome back, sir!" "It's good to see you again, Colonel!" "You can see us, right?"

"Yeah, I can see you," I replied, and I heard whoops of joy. "I'm in a hospital, right?"

The old man nodded. "You're a bit dazed, I think, Mustang. Don't worry."

Mustang? Was that me?

"Sir?" asked the blonde woman. "Are you okay?"

I looked at her, confused.

"Who are you?"


	2. Tell Me Who You Are

_Previous Chapter:_

 _"Sir?" asked the blonde woman. "Are you okay?"_

 _I looked at her, confused._

 _"Who are you?"_

* * *

 _ **Chapter 2 - Tell Me Who You Are**_

* * *

"Who are you?"

There was complete silence as my voice rang out throughout the whole ward. The blonde woman's smile faded a little, and her hand lowered. "Sir, don't play jokes with us…"

"'Sir'? Do I have some rank or something?" I asked, confused. "I don't know what you're talking about."

The blonde woman backed away, confused. I was confused too. Yes, sure, she was pretty, beautiful in fact, but I didn't remember her in my life. In fact, did I remember anything at all?

"Sir," spoke up an overweight man, with brown hair, "Colonel Mustang…" He smiled, but I heard from his tone he sounded quite a bit nervous. "Stop joking with us, sir… you're ruining the moment…"

"Moment? What moment?" I blinked. I remembered I'd heard that name again. _Mustang…_ "Mustang. You're talking about me, right?" I pointed my index finger to my chest.

"Yeah," said a black-haired man with glasses. "You're Colonel Mustang… remember?"

I looked at him, then at the man who had spoken before, then the man next to him - a grey haired man, who looked older, then I looked back at the blonde woman. "I… I don't know who you are."

The blonde woman's lip trembled, and she approached me, her pretty brown eyes interlocking with mine. "Sir… please stop playing-"

"I'm not, I swear I'm not!" I held my hands up in exasperation. "Who are you? I don't know you!"

The blonde woman backed away from me. _Again._ She looked hurt. She looked sad. I said, "Look, I'm sorry, I didn't know, but I'm telling the truth-"

I said those words quite fast, quite quick, nervous and flustered was what I'd felt.

The old man who had asked me about a 'Philosopher's Stone' (yes, was that what he had called it? Yeah.) approached me. "You don't know us?"

I shook my head with strong conviction. "I've never seen you before in my life. At least… I _don't_ remember meeting you before-"

"Surely you at least know the names of your friends? Or their faces?" The old man asked. His voice was gentle, but his tone sounded troubled.

"Friends?" I pointed at the group of men, and the blonde woman. "I - they're not my friends!"

 _Oh, I had realised too late on my mistake._

 _Oh, God._ I saw their faces fall and look hurt and sad. _Oh, no. Oh, please, no…_

"I - I'm sorry, you guys, but… I don't know you, I don't remember ever seeing you…"

The man with glasses sniffed sadly, and pointed at the blonde-haired woman. "Not even… don't you even remember her?" She looked sad, not on the verge of tears… no, that wasn't quite right. She didn't seem like the person to cry on the outside, especially not in front of people, whether she knew them or not.

I had no memory of her. I didn't know her. Who was she?

I shook my head, and I attempted to lock eyes with her, but she turned away, now expressionless. "Please," I said, in a mixture of sadness, slight curiosity and worry, "Tell me who you are."

The old man frowned even more. "Remember? I'm Doctor Marcoh, I offered you the Stone."

I shook my head at this Marcoh person. "I don't remember you… and the Stone. What's a rock got to do with this… mess?" I didn't know a better word for mess. I mean, I was in a mess. That was probably the only reason why I used that one certain word.

"I… I gave you the Philosopher's Stone. I created the transmutation circle-"

"Excuse me, what?"

Marcoh sighed, and I heard him mutter, "Maybe… maybe he's a bit…" he turned to me. "Close your eyes, Colonel Mustang."

I did as he asked. It was dark. And pitch-black. For a second, for one tiny, fleeting moment, I felt as if I'd felt it before. Darkness… and pain… but it had vanished from my memory as soon as it had appeared.

Marcoh's voice brought me back to the present. "Remember… what happened before you woke up… what you were doing… what you remember… remember… "

 _Remember… remember…_ that word. _Remember._ It echoed in my head, bounced around my mind as if on a trampoline. I shut my eyes tighter, and thought extremely hard. Now, what had I been doing? Think… _think…_ remember… _remember!_

But I didn't remember those faces. Who were they? They seemed to be my friends… they'd seem to _care_ for me as I woke up… they seemed overjoyed. But as I declared I knew nothing of them, that they weren't my friends, that joy that spread on their faces became sadness, worry, despair.

And as for me _?_ _I didn't even know my damn name!_ It was Mustang, right? Mustang… yeah. But I had known it because _someone else_ had told me. They said I was a Colonel, and they called me 'sir'. Was I some high-ranking official? But they were also my _friends…_ were they?

And I was hurt. I was in a hospital. Why? I knew my hands were bandaged… I felt wounds under my clothes. But what had caused them? I didn't understand...

I opened my eyes. "No," I said with finality. "I don't know. I don't remember. Please…"

The sentence wavered off. What was I going to say? _Please tell me who you are? Please tell me who I am? Please tell me what I'm doing here? Please forgive me because I just denied that I knew you and that I have no idea what the heck's just happened to me?_

I felt like a complete idiot.

Marcoh sighed, and glanced sadly at the group of people who were my 'friends', the faces unreadable. At least, unreadable to _me._ "Wait here. I'll have to report this. I can't believe this… could it be because…"

I didn't hear the rest, partially because he was out of earshot, partially because he had lowered his voice a little, and partially because I slightly didn't feel like I wanted to hear anymore. The door closed, and the little group and me were left alone.

Silence. A long silence. I didn't feel like I wanted to start the conversation. The others didn't seem like they wanted to, either.

I tried to look up at one of my friends, the grey-haired man. "Mustang. That's… my name, right?"

I wanted proof. I wanted proof I was at least a _being_ in the world.

He nodded. "Mustang. Roy Mustang."

"I didn't know."

I buried my face into my hands, not because I was, or wanted the assumption that, I was in deep thought, but because I had a little proof, a little clue, a simple, little thing of my past that I knew. _Roy Mustang…_ a name. _My_ name. _I was Roy Mustang._ It sounded so wonderful to me. But how about everyone else?

Looking up, I slowly asked, "So… if I'm… if I'm Roy Mustang… who… who are you? Please…" The last word seemed like I was begging. And, thinking back on it, I think I was. Begging for at least _something_ to help me remember.

The grey-haired man sighed. "I'm Falman, Vato Falman."

"Heymans Breda." The overweight man looked at me, then looked away.

"Kain Fuery, that's me," replied the dark-haired man with glasses.

None of them smiled, nor their voices filled with the usual warmth when meeting a new friend. Well, I _was_ their friend, and after that horrible re-encounter, how was I supposed to judge? It may have not been my fault with the memory and everything, but _I_ was the one that led them to this.

"And…?" I pointed at the blonde haired woman. Yes, I know it was rude, but still. I needed her attention. She refused to look at me. She seemed more interested in the posters that ordered health and cleanliness in the hospital wards. Was she trying to avoid me? "Please, ma'am, tell me your name. I'm… Roy Mustang. Pleased to meet you." I resisted the urge to say _again,_ in the fear that I would offend her. It may have seemed weird I was introducing myself to someone I had once known, but still. I didn't know her now.

She sighed. "Hawkeye. Good to meet you." She said it stiffly, without turning around to look at me, back still turned at me, brown eyes focused on the posters, the view outside, and the IV drips. It didn't seem like she felt good meeting me... _again._

"I'd like your full name, Miss Hawkeye-"

"I'd rather if you call me just Hawkeye, if you wouldn't mind," she said coldly, back still turned.

"Hey, Lieutenant," said the man called Breda, approaching her, "I don't think you should act so cold towards him-"

Hawkeye sighed, and whispered something inaudible, then moved towards a hospital bed I figured was hers. It was next to mine, on my left. Breda sighed, and returned back to his original spot. _It was most likely about me,_ I thought miserably.

"I'll be heading off to sleep for an hour or two," Hawkeye said. She turned, placing the blankets upon her, back _still_ turned against me, and she made a sound no more.

Whether she was sleeping or not, I didn't know.

I asked Fuery, Falman and Breda a question, "What has she got against me? She's acting so cold to me… she wouldn't even… but before, when I woke up, she seemed so _nice._ Are we enemies?"

"The opposite, sir," replied Falman gloomily. "You and she… don't be so hard on her. It's not her fault. She…"

"What?" I wanted to hear more.

"Nothing, s- Mustang. We'll leave you now."

And one by one, the three men filed out of the room.

* * *

I'd been looking out of my window, onto the view of a bustling city. I had no memories of it; I didn't remember if I'd done anything significant in it.

The city was partially in ruins. Some buildings were turned to rubble, some with just smashed windows, but as it grew closer to the place where I figured was the heart of the city, there was more rubble, debris and smoke. But then… was _I_ part of the mess? Was _that_ part of why I was in the hospital?

Suddenly, it was almost as if a jolt of electricity had suddenly erupted in my mind. _Something_ had _happened in Central City…_ _there was a battle… right? I… I…_ The thoughts disappeared as soon as they came. It irritated me like hell, and I didn't even understand too much what was happening. Within moments later, I had forgotten.

I turned almost instantly as soon as I heard the door open. It was a nurse, with fair hair and skin, holding two blue trays of food. She walked up to me, saying, "Here are your snacks, sir," then headed towards Hawkeye's bed before I had the chance to say a word of thanks.

Hawkeye was still sleeping, probably. I couldn't see her face; her back was still turned from me. I still wondered what had made her instantly dislike me so much. But she was the first sight I saw when I opened my eyes was her. She was smiling, holding out her hand. She said to me, "Welcome back, sir." Did something happen before? Had I made her angry during that short period of time? Maybe.

Then I remembered what I had said. _I - I'm sorry, you guys, but… I don't know you, I don't remember ever seeing you… Who are you? I don't know you! Friends? I - they're not my friends!_

I picked up a biscuit and chewed it slowly, thinking hard. What were the names of the other three men, the three men all looking overjoyed to see him? Oh, yeah - Fuery, Breda and Falman. They seemed like my friends too… right? I wished I remembered them. I thought long and hard, closing my eyes tightly as I had did before; still I remembered nothing.

I glanced at Hawkeye, then in my head, I heard a tiny voice, _It's okay. You can trust her. It's okay. It's okay…_ I closed my eyes. My memory was still a blank, but through searching my mind, I assumed Hawkeye was a close friend, if not someone special in my life. I could trust her. Could I trust the three men, too? Could I? My mind told me 'yes'. I could.

But it had to start with regaining my memory, who I was before. Just knowing my name, _Roy Mustang,_ wasn't going to cut it.

I needed to know who I was, my past, my life. I needed to know my friends, my enemies. And to get back Hawkeye's friendship. I _needed_ it. I _wanted_ it. I wanted to be her friend again. It hadn't occurred to me why it was so significant, besides my experience when I had opened my eyes and lost my memory, but I wanted her friendship badly. I'd broken it - so I had to fix it.

There was still hope. It was just the beginning.

The beginning of many things to come.

* * *

 _ **Well, well! How was that? The chapters will be longer as the story progresses, but I do hope I did a good job.**_

 ** _I don't think I'll spoil too many things right now. I'd like you all to favourite, follow, or at least drop a review, but I like this story so much, that I'll finish it, no matter who's reading it or how popular it is._**

 ** _Oh! And if you have any story requests for me, I'll be waiting for them! Guidelines on my bio and all that... but anyways..._**

 ** _Thanks for reading Chapter 2, Chapter 3 hopefully coming soon!_**


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